Methods and systems to correlate arrhythmic and ischemic events

ABSTRACT

Systems and methods for determining whether there is a correlation between arrhythmias and myocardial ischemic episodes are provided. An implantable system (e.g., a monitor, pacemaker or ICD) is used to monitor for arrhythmias and to monitor for myocardial ischemic episodes. When such events are detected by the implantable system, the implantable system stores (e.g., in its memory) data indicative of the detected arrhythmias and data indicative of the detected myocardial, ischemic episodes. Then, for each detected arrhythmia, a determination is made based on the data, whether there was a myocardial ischemic episode detected within a specified temporal proximity of (e.g., within a specified amount of time of) the arrhythmia. Where a myocardial ischemic episode occurred within the specified temporal proximity of an arrhythmia, data for the two events can be linked. Additionally, when a log of arrhythmias is displayed, for each arrhythmia there is an indication of whether a myocardial ischemic episode was detected within the specified temporal proximity of the arrhythmia. This abstract is not intended to be a complete description of, or limit the scope of, the invention.

PRIORITY CLAIM

This application is a Continuation application of and claims priorityand other benefits from U.S. patent application Ser. No. 11/198,781, nowU.S. Pat. No. 7,706,867, filed Aug. 4, 2005, entitled “METHODS ANDSYSTEMS TO CORRELATE ARRHYTHMIC AND ISCHEMIC EVENTS”, incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to implantable cardiacstimulation devices capable of myocardial ischemia and arrhythmiamonitoring.

BACKGROUND OF THE INVENTION

Implantable cardiac stimulation devices are currently being used totreat various types of arrhythmias, such as ventricular tachycardia (VT)and ventricular fibrillation (VF). Such devices are capable of detectingthe occurrence of an arrhythmia, and automatically applying anappropriate electrical stimulation or shock therapy to the heart aimedat terminating the detected arrhythmia. In addition to providingautomatic stimulation, such devices often include a data acquisitionsystem that is configured to acquire intracardiac electrogram (IEGM)signals, convert the raw analog data into digital signals, and store thedigital signals for later processing and/or telemetric transmission toan external device.

Recently, there been increased interest in adding myocardial ischemiadetection capabilities to implantable cardiac devices. Myocardialischemia, which involves oxygen starvation of the myocardium, can leadto myocardial infarction (MI) and/or the onset of malignant arrhythmiasif the oxygen starvation is not alleviated. Although myocardial ischemiais sometimes associated with the symptom of angina pectoris (i.e., chestpain), may episodes of myocardial ischemia are asymptomatic or “silent.”The inclusion of myocardial ischemia detection capabilities within animplantable device can provide a physician with information about apatient's ischemic burden, which is especially useful when the patientis suffering from silent ischemia.

While trending of ongoing ischemia burden is of interest, it has so farbeen unclear how to make such information actionable by a physician forthings other than detection of risk of an acute myocardial infarction(MI). In other words, it is still generally unclear when a patient'schronic ischemic condition has grown bad enough to warrant pharmacologictherapy, or an angioplasty or coronary artery bypass procedure.Currently, it is likely that the physician will have to rely as much ormore on patient symptomatology as on implantable device diagnostics tomake such a determination. However, if it could be demonstrated thattransient ischemic episodes were precipitating an increase inpotentially lethal arrhythmias, a physician might deem such informationas sufficient reason to intervene, regardless of the presence or absenceof symptoms such as chest pain. Accordingly, there is a desire toprovide physicians with information that will allow them to readilyidentify correlations between ischemic episodes and arrhythmias.

SUMMARY OF THE INVENTION

Embodiments of the present invention are related to systems and methodsfor determining whether there is a correlation between arrhythmias andmyocardial ischemic episodes experienced by a patient. In accordancewith embodiments of the present invention, an implantable system (e.g.,a monitor, pacemaker or ICD) is used to monitor for arrhythmias and tomonitor for myocardial ischemic episodes. When such events are detectedby the implantable system, the implantable system stores (e.g., in itsmemory) data indicative of the detected arrhythmias and data indicativeof the detected myocardial ischemic episodes. Then, for each detectedarrhythmia, a determination is made based on the data, whether there wasa myocardial ischemic episode detected within a specified temporalproximity of (e.g., within a specified amount of time of) thearrhythmia. In a specific example, there is a determination of whetherthere was one or more myocardial ischemic episode detected within thefour hours leading up to an arrhythmia. This determination can beperformed by the implantable system, but is preferably performed by anon-implanted system (e.g., a device programmer) that receives (e.g.,uploads) the stored data from the implanted system.

In accordance with specific embodiments of the present invention, when amyocardial ischemic episode is detected within the specified temporalproximity of a detected arrhythmia, data indicative of the detectedmyocardial ischemic episode is linked with data indicative of thearrhythmia. This enables a user observing information about one type ofevent (e.g., an arrhythmia) to easily observe information about theother type of event (e.g., a myocardial ischemic episode), when theseevents occur within the specified temporal proximity to one another.

Certain embodiments of the present invention involve displaying a log ofdetected arrhythmias that indicates, for each arrhythmia, whether therewas a myocardial ischemic episode detected within the specified temporalproximity of the arrhythmia. Preferably, a user observing the log canselect one of the arrhythmias from the log. When a myocardial ischemicevent was detected within the specified temporal proximity to theselected arrhythmia, information about the selected arrhythmia andinformation about the myocardial ischemic episode are both displayed.This will assist the user (e.g., a physician, clinician or technician)with determining whether one or more myocardial ischemic episode mayhave precipitated an arrhythmia.

Alternatively, or additionally, a log of detected myocardial ischemicepisodes is displayed, wherein the log indicates, for each ischemicepisode, whether there was an arrhythmia within the specified temporalproximity of the ischemic episode. Similarly, a user can select one ofthe myocardial ischemic episodes from the log, such that when anarrhythmia was detected within the specified temporal proximity to theselected myocardial ischemic episode, information about the selectedmyocardial ischemic episode and the arrhythmia are both displayed.

In accordance with other embodiments of the present invention, animplantable system is used to monitor for arrhythmias and to store,within the implantable system, data indicative of a detected arrhythmiaand data indicative of a specified period leading up to the arrhythmia.Such data is then transmitted (periodically, or when the patient visitsa physician's office) from the implantable system to a non-implantedsystem. For each arrhythmia, the non-implanted system can then determinebased on the data indicative of the specified period leading up to thearrhythmia, whether there was a myocardial ischemic episode detectedwithin the specified period leading up to the arrhythmia.

This summary is not intended to be a complete description of theinvention. Other features and advantages of the invention will appearfrom the following description in which the preferred embodiments havebeen set forth in detail, in conjunction with the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified, partly cutaway view illustrating an implantablestimulation device in electrical communication with at least three leadsimplanted into a patient's heart for delivering multi-chamberstimulation and shock therapy.

FIG. 2 is a functional block diagram of the multi-chamber implantablestimulation device of FIG. 1, illustrating the basic elements thatprovide pacing stimulation, cardioversion, and defibrillation in fourchambers of the heart.

FIG. 3 is a functional block diagram of an exemplary external programmerdevice that can be used to program the implantable device of FIGS. 1 and2, and to upload and analyze data collected by the implantable device.

FIG. 4 is a high level flow diagram illustrating methods for determiningcorrelations between arrhythmias and ischemic episodes, in accordancewith embodiments of the present invention.

FIGS. 5 and 6 are high level flow diagrams that illustrates howinformation about arrhythmias and ischemic episodes can be displayed toa user in such a manner that a temporal relationship between the two areimmediately apparent to the observer.

FIG. 7 illustrates an exemplary display log of detected arrhythmias thatincludes indications of whether there was a myocardial ischemic episodewithin a specified temporal proximity of each arrhythmia.

FIG. 8 illustrates an exemplary graph of detected arrhythmias andischemic episodes that enables a person to see, at a glance, when amyocardial ischemic episode occurred within a specified temporalproximity of an arrhythmia.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following description includes a best mode presently contemplatedfor the device. This description is not to be taken in a limiting sensebut is made merely for the purpose of describing the general principlesof the device. In the description that follows, like numerals orreference designators will be used to refer to like parts or elementsthroughout.

The disclosed systems and methods are directed to correlating arrhythmicand myocardial ischemic events. Thus, the methods described herein areintended for use with any implantable cardiac device capable ofdetecting arrhythmias and myocardial ischemic episodes. An exemplaryimplantable cardiac device will thus be described in conjunction withFIGS. 1 and 2, in which embodiments of the present invention describedherein could be implemented. Additionally, FIG. 3 will be used todescribed an exemplary external programmer that can be used to programan implantable cardiac device, as well as upload information fromimplantable cardiac devices and analyze such information. It isrecognized, however, that numerous variations of such a device exist inwhich the methods could be implemented.

Referring to FIG. 1, an exemplary implantable device 110 (also referredto as a pacing device, a pacing apparatus, a stimulation device, orsimply a device) is in electrical communication with a patient's heart112 by way of three leads, 120, 124 and 130, suitable for deliveringmulti-chamber stimulation. While not necessary to perform embodiments ofthe present invention, the exemplary device 110 is also capable ofdelivering shock therapy.

To sense atrial cardiac signals and to provide right atrial chamberstimulation therapy, the stimulation device 110 is coupled to animplantable right atrial lead 120 having at least an atrial tipelectrode 122, which typically is implanted in the patient's rightatrial appendage. To sense left atrial and ventricular cardiac signalsand to provide left-chamber pacing therapy, the stimulation device 110is coupled to a “coronary sinus” lead 124 designed for placement in the“coronary sinus region” via the coronary sinus for positioning a distalelectrode adjacent to the left ventricle and/or additional electrode(s)adjacent to the left atrium. As used herein, the phrase “coronary sinusregion” refers to the vasculature of the left ventricle, including anyportion of the coronary sinus, great cardiac vein, left marginal vein,left posterior ventricular vein, middle cardiac vein, and/or smallcardiac vein or any other cardiac vein accessible by the coronary sinus.

Accordingly, an exemplary coronary sinus lead 124 is designed to receiveleft atrial and ventricular cardiac signals and to deliver left atrialand ventricular pacing therapy using at least a left ventricular tipelectrode 126, left atrial pacing therapy using at least a left atrialring electrode 127, and shocking therapy using at least a left atrialcoil electrode 128. The present invention may of course be practicedwith a coronary sinus lead that does not include left atrial sensing,pacing or shocking electrodes.

The stimulation device 110 is also shown in electrical communicationwith the patient's heart 112 by way of an implantable right ventricularlead 130 having, in this embodiment, a right ventricular tip electrode132, a right ventricular ring electrode 134, a right ventricular (RV)coil electrode 136, and an SVC coil electrode 138. Typically, the rightventricular lead 130 is transvenously inserted into the heart 112 so asto place the right ventricular tip electrode 132 in the rightventricular apex so that the RV coil electrode 136 will be positioned inthe right ventricle and the SVC coil electrode 138 will be positioned inthe superior vena cava. Accordingly, the right ventricular lead 130 iscapable of receiving cardiac signals and delivering stimulation in theform of pacing and shock therapy to the right ventricle. It will beunderstood by those skilled in the art that other lead and electrodeconfigurations such as epicardial leads and electrodes may be used inpracticing the invention.

As illustrated in FIG. 2, a simplified block diagram is shown of themulti-chamber implantable implantable device 110, which is capable oftreating both fast and slow arrhythmias with stimulation therapy,including pacing, cardioversion and defibrillation stimulation. While aparticular multi-chamber device is shown, this is for illustrationpurposes only, and one of skill in the art could readily duplicate,eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with pacing, cardioversion and defibrillation stimulation.

The housing 240 for the implantable device 110, shown schematically inFIG. 2, is often referred to as the “can”, “case” or “case electrode”and may be programmably selected to act as the return electrode for all“unipolar” modes. The housing 240 may further be used as a returnelectrode alone or in combination with one or more of the coilelectrodes, 128, 136 and 138, for shocking purposes. The housing 240further includes a connector (not shown) having a plurality ofterminals, 242, 244, 246, 248, 252, 254, 256, and 258 (shownschematically and, for convenience, the names of the electrodes to whichthey are connected are shown next to the terminals). As such, to achieveright atrial sensing and pacing, the connector includes at least a rightatrial tip terminal (A_(R) TIP) 242 adapted for connection to the atrialtip electrode 122.

To achieve left atrial and ventricular sensing, pacing and shocking, theconnector includes at least a left ventricular tip terminal (V_(L) TIP)244, a left atrial ring terminal (A_(L) RING) 246, and a left atrialshocking terminal (A_(L) COIL) 148, which are adapted for connection tothe left ventricular ring electrode 126, the left atrial tip electrode127, and the left atrial coil electrode 128, respectively.

To support right ventricle sensing, pacing and shocking, the connectorfurther includes a right ventricular tip terminal (V_(R) TIP) 252, aright ventricular ring terminal (V_(R) RING) 254, a right ventricularshocking terminal (R_(V) COIL) 256, and an SVC shocking terminal (SVCCOIL) 258, which are adapted for connection to the right ventricular tipelectrode 132, right ventricular ring electrode 134, the RV coilelectrode 136, and the SVC coil electrode 138, respectively.

At the core of the implantable device 110 is a programmablemicrocontroller 260 which controls the various types and modes ofstimulation therapy. As is well known in the art, the microcontroller260 typically includes a microprocessor, or equivalent controlcircuitry, designed specifically for controlling the delivery ofstimulation therapy and can further include RAM or ROM memory, logic andtiming circuitry, state machine circuitry, and I/O circuitry. Typically,the microcontroller 260 includes the ability to process or monitor inputsignals (data) as controlled by a program code stored in a designatedblock of memory. The details of the design of the microcontroller 260are not critical to the present invention. Rather, any suitablemicrocontroller 260 can be used to carry out the functions describedherein. The use of microprocessor-based control circuits for performingtiming and data analysis functions are well known in the art. Inspecific embodiments of the present invention, the microcontroller 260performs some or all of the steps associated with arrhythmia detectionand myocardial ischemia detection.

Representative types of control circuitry that may be used with theinvention include the microprocessor-based control system of U.S. Pat.No. 4,940,052 (Mann et. al.) and the state-machines of U.S. Pat. No.4,712,555 (Sholder) and U.S. Pat. No. 4,944,298 (Sholder). For a moredetailed description of the various timing intervals used within thepacing device and their inter-relationship, see U.S. Pat. No. 4,788,980(Mann et. al.). The '052, '555, '298 and '980 patents are incorporatedherein by reference.

An atrial pulse generator 270 and a ventricular pulse generator 272generate pacing stimulation pulses for delivery by the right atrial lead120, the right ventricular lead 130, and/or the coronary sinus lead 124via an electrode configuration switch 274. It is understood that inorder to provide stimulation therapy in each of the four chambers of theheart, the atrial and ventricular pulse generators, 270 and 272, mayinclude dedicated, independent pulse generators, multiplexed pulsegenerators, or shared pulse generators. The pulse generators, 270 and272, are controlled by the microcontroller 260 via appropriate controlsignals, 276 and 278, respectively, to trigger or inhibit thestimulation pulses.

The microcontroller 260 further includes timing control circuitry 279which is used to control pacing parameters (e.g., the timing ofstimulation pulses) as well as to keep track of the timing of refractoryperiods, noise detection windows, evoked response windows, alertintervals, marker channel timing, etc., which is well known in the art.Examples of pacing parameters include, but are not limited to,atrio-ventricular delay, interventricular delay and interatrial delay.

The switch bank 274 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch 274, inresponse to a control signal 280 from the microcontroller 260,determines the polarity of the stimulation pulses (e.g., unipolar,bipolar, etc.) by selectively closing the appropriate combination ofswitches (not shown) as is known in the art.

Atrial sensing circuits 282 and ventricular sensing circuits 284 mayalso be selectively coupled to the right atrial lead 120, coronary sinuslead 124, and the right ventricular lead 130, through the switch 274 fordetecting the presence of cardiac activity in each of the four chambersof the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR.SENSE) sensing circuits, 282 and 284, may include dedicated senseamplifiers, multiplexed amplifiers, or shared amplifiers. The switch 274determines the “sensing polarity” of the cardiac signal by selectivelyclosing the appropriate switches, as is also known in the art. In thisway, the clinician may program the sensing polarity independent of thestimulation polarity.

Each sensing circuit, 282 and 284, preferably employs one or more lowpower, precision amplifiers with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit, as knownin the art, to selectively sense the cardiac signal of interest. Theautomatic gain control enables the device 110 to deal effectively withthe difficult problem of sensing the low amplitude signalcharacteristics of atrial or ventricular fibrillation. Such sensingcircuits, 282 and 284, can be used to determine cardiac performancevalues used in the present invention. Alternatively, an automaticsensitivity control circuit may be used to effectively deal with signalsof varying amplitude.

The outputs of the atrial and ventricular sensing circuits, 282 and 284,are connected to the microcontroller 260 which, in turn, are able totrigger or inhibit the atrial and ventricular pulse generators, 270 and272, respectively, in a demand fashion in response to the absence orpresence of cardiac activity, in the appropriate chambers of the heart.The sensing circuits, 282 and 284, in turn, receive control signals oversignal lines, 286 and 288, from the microcontroller 260 for purposes ofmeasuring cardiac performance at appropriate times, and for controllingthe gain, threshold, polarization charge removal circuitry (not shown),and timing of any blocking circuitry (not shown) coupled to the inputsof the sensing circuits, 282 and 286.

For arrhythmia detection, the device 110 includes an arrhythmia detector262 that utilizes the atrial and ventricular sensing circuits, 282 and284, to sense cardiac signals to determine whether a rhythm isphysiologic or pathologic. The timing intervals between sensed events(e.g., P-waves, R-waves, and depolarization signals associated withfibrillation) are then classified by the microcontroller 260 bycomparing them to a predefined rate zone limit (i.e., bradycardia,normal, low rate VT, high rate VT, and fibrillation rate zones) andvarious other characteristics (e.g., sudden onset, stability,physiologic sensors, and morphology, etc.) in order to assist withdetermining the type of remedial therapy that is needed (e.g.,bradycardia pacing, anti-tachycardia pacing, cardioversion shocks ordefibrillation shocks, collectively referred to as “tiered therapy”).The arrhythmia detector 262 can be implemented within themicrocontroller 260, as shown in FIG. 2. Thus, this detector 262 can beimplemented by software, firmware, or combinations thereof. It is alsopossible that all, or portions, of the arrhythmia detector 262 can beimplemented using hardware. Further, it is also possible that all, orportions, of the ischemia detector 262 can be implemented separate fromthe microcontroller 260.

Two exemplary types of arrhythmias that the arrhythmia detector 262 candetect include ventricular tachycardia (VT) and ventricular fibrillation(VF). A tachycardia is a fast heart rate (usually over 100 beats perminute) typically caused by disease or injury. It can also be part of anormal response to increased activity or oxygen demands. The averageheart beats between 60 and 100 times per minute. When the tachycardia isdue to disease or injury, it usually requires treatment. Tachycardiasmay begin in the upper chambers of the heart (the atria) or the lowerchambers of the heart (the ventricles). A ventricular tachycardia (VT)begins in the ventricles. Some are harmless, but others are lifethreatening in that they can quickly deteriorate to a ventricularfibrillation.

A ventricular fibrillation (VF) is a very fast, chaotic heart rate(usually over 102 beats per minute) in the lower chambers of the heart,resulting from multiple areas of the ventricles attempting to controlthe heart's rhythm. VF can occur spontaneously (generally caused byheart disease) or when VT has persisted too long. When the ventriclesfibrillate, they do not contract normally, so they cannot effectivelypump blood. The instant VF begins, effective blood pumping stops. VFquickly becomes more erratic, resulting in sudden cardiac arrest. Thisarrhythmia must be corrected immediately via a shock from an externaldefibrillator or an implantable cardioverter defibrillator (ICD). Thedefibrillator stops the chaotic electrical activity and restores normalheart rhythm.

These are just two examples of the types of arrhythmias that thearrhythmia detector 262 can detect. One of ordinary skill in the artwill appreciate that other types of arrhythmias can be detected, andinformation for such other types of arrhythmias can be stored. Examplesof other types of arrhythmias that can be detected by the detector 262include, but are not limited to, supraventricular arrhythmias (SVAs) andatrial arrhythmias such as atrial fibrillation (AF).

In accordance with embodiments of the present invention, the implantabledevice 110 can store, in memory 294, IEGM data corresponding to theperiod immediately prior to, during and subsequent to a detectedarrhythmia. The implantable device can also store data that identifiesthe type of arrhythmia, the time of the arrhythmia (e.g., a time stamp),the duration of the arrhythmia, as well as any other type of informationthat a physician may deem useful. U.S. Pat. No. 4,295,474 (Fischell) andU.S. Pat. No. 5,732,708 (Nau et al.), each of which is incorporatedherein by reference, provide exemplary additional details of the typesof data that can be stored in response to the detection of an arrhythmia(and other cardiac events), and how such data can be efficiently andeffectively stored. Using embodiments of the present invention, aphysician can demonstrate when ischemic episodes may be precipitating anincrease in potentially lethal arrhythmias, and thus, when to intervene(e.g., using pharmacologic therapy, an angioplasty or coronary arterybypass procedure), regardlest of the presence or absence of symptomssuch as chest pain.

In accordance with embodiments of the present invention, the implantabledevice 110 also includes an ischemia detector 264, which as described inmore detail below, can detect ischemic events based, e.g., on ST-segmentshift analysis. The ischemia detector 264 can be implemented within themicrocontroller 260, as shown in FIG. 2. Thus, this detector 264 can beimplemented by software, firmware, or combinations thereof. It is alsopossible that all, or portions, of the ischemia detector 264 can beimplemented using hardware. Further, it is also possible that all, orportions, of the ischemia detector 264 can be implemented separate fromthe microcontroller 260.

The ischemia detector 264 can monitor sensed cardiac signals in order todetect and record timing and duration information relating to myocardialischemic episodes. Ischemia detector 264 may also trigger a patient orphysician alert in response to detecting a myocardial ischemic event.For example, a patient alert 219, which produces a vibratory or auditoryalert, may be triggered.

There are many documented techniques for detecting episodes ofmyocardial ischemia. Many of these techniques perform ST-segment shiftanalysis to determine if there is a deviation of the ST-segment from abaseline (e.g., a PQ segment baseline), and detect myocardial ischemicevents when the deviation is beyond a threshold. Other techniques arealso possible. The precise technique used by the ischemia detector 264to detect episodes of myocardial ischemia are not important to thepresent invention. Rather, what is important is that the ischemiadetector 264 can detect episodes of myocardial ischemia and causeinformation relating to these episodes to be stored. For example, theimplantable device 110 can store, in memory 294, IEGM data correspondingto the period immediately prior to, during and subsequent to a detectedmyocardial ischemic episode. The implantable device can also store datathat identifies the ST-segment level during various portions of anepisode (e.g., at onset of the ischemia, the peak of the ischemia andthe termination of the ischemia), the time of the ischemic episodes (atonset, at peak and/or at termination), the duration of the episode, aswell as any other type of information that a physician may deem useful.U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023 (all to Fischell etal.), which are incorporated herein by reference, provide exemplaryadditional details of the types of data that can be stored in responseto the detection of a myocardial ischemic episode, and how such data canbe efficiently and effectively stored.

Embodiments of the present invention, as will be described in moredetail below, determine, or assist with the determination of, whetherthere is a correlation between arrhythmias and myocardial ischemicepisodes experienced by a patient. Such information will enable amedical practitioner to analyze whether ischemic episodes that thepatient experienced may have precipitated arrhythmias.

Still referring to FIG. 2, cardiac signals are also applied to theinputs of an analog-to-digital (A/D) data acquisition system 290. Thedata acquisition system 290 is configured to acquire intracardiacelectrogram signals, convert the raw analog data into a digital signal,and store the digital signals for later processing and/or telemetrictransmission to an external device 202. The data acquisition system 290is coupled to the right atrial lead 120, the coronary sinus lead 124,and the right ventricular lead 130 through the switch 274 to samplecardiac signals across any pair of desired electrodes. In specificembodiments, the data acquisition system 290 may be used to acquire IEGMsignals for the analysis of changes in the ST-segment for detectingmyocardial ischemia.

The data acquisition system 290 can be coupled to the microcontroller260, or other detection circuitry, for detecting an evoked response fromthe heart 112 in response to an applied stimulus, thereby aiding in thedetection of “capture”. Capture occurs when an electrical stimulusapplied to the heart is of sufficient energy to depolarize the cardiactissue, thereby causing the heart muscle to contract. Themicrocontroller 260 detects a depolarization signal during a windowfollowing a stimulation pulse, the presence of which indicates thatcapture has occurred. The microcontroller 260 enables capture detectionby triggering the ventricular pulse generator 272 to generate astimulation pulse, starting a capture detection window using the timingcontrol circuitry 279 within the microcontroller 260, and enabling thedata acquisition system 290 via control signal 292 to sample the cardiacsignal that falls in the capture detection window and, based on theamplitude, determines if capture has occurred.

The implementation of capture detection circuitry and algorithms arewell known. See for example, U.S. Pat. No. 4,729,376 (Decote, Jr.); U.S.Pat. No. 4,708,142 (Decote, Jr.); U.S. Pat. No. 4,686,988 (Sholder);U.S. Pat. No. 4,969,467 (Callaghan et. al.); and U.S. Pat. No. 5,350,410(Mann et. al.), which patents are hereby incorporated herein byreference. The type of capture detection system used is not critical tothe present invention.

The microcontroller 260 is further coupled to the memory 294 by asuitable data/address bus 296, wherein the programmable operatingparameters used by the microcontroller 260 are stored and modified, asrequired, in order to customize the operation of the implantable device110 to suit the needs of a particular patient. Such operating parametersdefine, for example, pacing pulse amplitude, pulse duration, electrodepolarity, rate, sensitivity, automatic features, arrhythmia detectioncriteria, and the amplitude, waveshape and vector of each shocking pulseto be delivered to the patient's heart 112 within each respective tierof therapy.

The operating parameters of the implantable device 110 may benon-invasively programmed into the memory 294 through a telemetrycircuit 201 in telemetric communication with an external device 202,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 201 can be activated by themicrocontroller 260 by a control signal 206. The telemetry circuit 201advantageously allows intracardiac electrograms and status informationrelating to the operation of the device 110 (as contained in themicrocontroller 260 or memory 294) to be sent to the external device 202through an established communication link 204.

For examples of such devices, see U.S. Pat. No. 4,809,697, entitled“Interactive Programming and Diagnostic System for use with ImplantablePacemaker” (Causey, III et al.); U.S. Pat. No. 4,944,299, entitled “HighSpeed Digital Telemetry System for Implantable Device” (Silvian); andU.S. Pat. No. 6,275,734 entitled “Efficient Generation of SensingSignals in an Implantable Medical Device such as a Pacemaker or ICD”(McClure et al.), which patents are hereby incorporated herein byreference.

The implantable device 110 additionally includes a battery 211 whichprovides operating power to all of the circuits shown in FIG. 2. If theimplantable device 110 also employs shocking therapy, the battery 211should be capable of operating at low current drains for long periods oftime, and then be capable of providing high-current pulses (forcapacitor charging) when the patient requires a shock pulse. The battery211 should also have a predictable discharge characteristic so thatelective replacement time can be detected.

The implantable device 110 can also include a magnet detection circuitry(not shown), coupled to the microcontroller 260. It is the purpose ofthe magnet detection circuitry to detect when a magnet is placed overthe implantable device 110, which magnet may be used by a clinician toperform various test functions of the implantable device 110 and/or tosignal the microcontroller 260 that the external programmer 202 is inplace to receive or transmit data to the microcontroller 260 through thetelemetry circuits 201.

As further shown in FIG. 2, the device 110 is also shown as having animpedance measuring circuit 213 which is enabled by the microcontroller260 via a control signal 214. The known uses for an impedance measuringcircuit 213 include, but are not limited to, lead impedance surveillanceduring the acute and chronic phases for proper lead positioning ordislodgement; detecting operable electrodes and automatically switchingto an operable pair if dislodgement occurs; measuring respiration orminute ventilation; measuring thoracic impedance for determining shockthresholds and heart failure condition; detecting when the device hasbeen implanted; measuring stroke volume; and detecting the opening ofheart valves, etc. The impedance measuring circuit 213 is advantageouslycoupled to the switch 274 so that any desired electrode may be used. Theimpedance measuring circuit 213 is not critical to the present inventionand is shown only for completeness.

In the case where the implantable device 110 is also intended to operateas an implantable cardioverter/defibrillator (ICD) device, it mustdetect the occurrence of an arrhythmia, and automatically apply anappropriate electrical shock therapy to the heart aimed at terminatingthe detected arrhythmia. To this end, the microcontroller 260 furthercontrols a shocking circuit 216 by way of a control signal 218. Theshocking circuit 216 generates shocking pulses of low (up to 0.5Joules), moderate (0.5-10 Joules), or high energy (11 to 40 Joules), ascontrolled by the microcontroller 260. Such shocking pulses are appliedto the patient's heart 112 through at least two shocking electrodes, andas shown in this embodiment, selected from the left atrial coilelectrode 228, the RV coil electrode 236, and/or the SVC coil electrode238. As noted above, the housing 240 may act as an active electrode incombination with the RV electrode 236, or as part of a split electricalvector using the SVC coil electrode 238 or the left atrial coilelectrode 228 (i.e., using the RV electrode as a common electrode).

The above described implantable device 110 was described as an exemplarypacing device. One or ordinary skill in the art would understand thatembodiments of the present invention can be used with alternative typesof implantable devices. Accordingly, embodiments of the presentinvention should not be limited to use only with the above describeddevice.

FIG. 3 will now be used to illustrate components of an exemplaryexternal programmer 202 for use in programming the implantable device110, uploading data from the implantable device, and analyzing suchdata. Briefly, the programmer permits a physician or other user toprogram the operation of the implantable device 110 and to retrieve anddisplay information received from the implantable device such as IEGMdata and device diagnostic data. Additionally, the external programmercan receive and display EKG data from separate external EKG leads thatmay be attached to the patient. As will be described in further detailbelow, in accordance with embodiments of the present invention, theexternal programmer 202 is capable of processing and analyzing datareceived from the implantable device 110.

Operations of the programmer 202 are controlled by a CPU 302, which maybe a generally programmable microprocessor or microcontroller or may bea dedicated processing device such as an application specific integratedcircuit (ASIC) or the like. Software instructions to be performed by theCPU are accessed via an internal bus 304 from a read only memory (ROM)306 and random access memory 330. Additional software may be accessedfrom a hard drive 308, floppy drive 310, and CD ROM drive 312, or othersuitable permanent mass storage device. Depending upon the specificimplementation, a basic input output system (BIOS) is retrieved from theROM by CPU at power up. Based upon instructions provided in the BIOS,the CPU “boots up” the overall system in accordance withwell-established computer processing techniques.

Once operating, the CPU 302 displays a menu of programming options tothe user via an LCD display 314 or other suitable computer displaydevice. To this end, the CPU may, for example, display a menu ofspecific programming parameters of the implantable device to beprogrammed or may display a menu of types of diagnostic data to beretrieved and displayed. In response thereto, the physician entersvarious commands via either a touch screen 316 overlaid on the LCDdisplay or through a standard keyboard 318 supplemented by additionalcustom keys 320, such as an emergency VVI (EVVI) key. The EVVI key setsthe implantable device to a safe VVI mode with high pacing outputs. Thisensures life sustaining pacing operation in nearly all situations but byno means is it desirable to leave the implantable device in the EVVImode at all times.

Once all pacing leads are mounted and the implantable device 110 isimplanted, the various devices are programmed. Typically, the physicianinitially controls the programmer 202 to retrieve data stored within anyimplantable device 110 and to also retrieve EKG data from EKG leads 332,if any, coupled to the patient. To this end, the CPU 302 transmitsappropriate signals to a telemetry subsystem 322, which providescomponents for directly interfacing with the implantable device 110, andthe EKG leads. Telemetry subsystem 322 includes its own separate CPU 324for coordinating the operations of the telemetry subsystem. Main CPU 302of programmer communicates with telemetry subsystem CPU 324 via internalbus 304. Telemetry subsystem 322 additionally includes a telemetrycircuit 326 connected to telemetry wand 328, which, in turn, receivesand transmits signals electromagnetically from the telemetry unit 201 ofthe implantable device 110. The telemetry wand 328 is placed over thechest of the patient near the implantable device to permit reliabletransmission of data between the telemetry wand 328 and the implantabledevice 110.

Typically, at the beginning of the programming session, the externalprogramming device 202 controls the implantable device 110 viaappropriate signals generated by the telemetry wand 328 to output allpreviously recorded patient and device diagnostic information. Patientdiagnostic information includes, for example, recorded IEGM data andstatistical patient data such as the percentage of paced versus sensedheartbeats. Device diagnostic data includes, for example, informationrepresentative of the operation of the implantable device such as leadimpedances, battery voltages, battery recommended replacement time (RRT)information and the like. Data retrieved from the implantable device 110is stored by external programmer 202 either within a random accessmemory (RAM) 330, hard drive 308 or within a floppy diskette placedwithin floppy drive 310. Additionally, or in the alternative, data maybe permanently or semi-permanently stored within a compact disk (CD) orother digital media disk, if the overall system is configured with adrive for recording data onto digital media disks, such as a write onceread many (WORM) drive.

Once all patient and device diagnostic data previously stored within theimplantable device 110 is transferred to programmer 202, the implantabledevice 110 may be further controlled to transmit additional data in realtime as it is detected by the implantable device 110, such as additionalIEGM data, lead impedance data, and the like. Additionally, or in thealternative, telemetry subsystem 322 receives EKG signals from EKG leads332 via an EKG processing circuit 334. As with data retrieved from theimplantable device itself, signals received from the EKG leads arestored within one or more of the storage devices of the externalprogrammer. Typically, EKG leads output analog electrical signalsrepresentative of the EKG. Accordingly, EKG circuit 334 includes analogto digital conversion circuitry for converting the signals to digitaldata appropriate for further processing within programmer. Dependingupon the implementation, the EKG circuit 334 may be configured toconvert the analog signals into event record data for ease of processingalong with the event record data retrieved from the implantable device.Typically, signals received from the EKG leads are received andprocessed in real time.

Thus, the programmer 202 can receive data both from the implantabledevice 110 and from the external EKG leads 332. As will be explained inmore detail below, in specific embodiments of the present invention theprogrammer 202 receive arrhythmia data and myocardial ischemic episodedata from the implantable device 110, thereby enabling the programmer202 to analyze and display such data.

Data retrieved from the implantable device 110 includes parametersrepresentative of the current programming state of the implantabledevice 110. Under the control of the physician, the external programmer202 displays the current programming parameters and permits thephysician to reprogram the parameters. To this end, the physician entersappropriate commands via any of the aforementioned input devices and,under control of CPU 302, the programming commands are converted tospecific programming parameters for transmission to the implantabledevice 110 via telemetry wand 328 to thereby reprogram the implantabledevice 110. A wide variety of parameters may be programmed by thephysician, including, but not limited to atrioventricular andinter-ventricular delay values. Prior to reprogramming specificparameters, the physician may control the external programmer 202 todisplay any or all of the data retrieved from the implantable device 110or from the EKG leads, including displays of ECGs, IEGMs, andstatistical patient information. Any or all of the information displayedby programmer may also be printed using a printer 336.

The programmer 202 also includes a modem 338 to permit directtransmission of data to other programmers via the public switchedtelephone network (PSTN) or other interconnection line, such as a T1line or fiber optic cable. Depending upon the implementation, the modemmay be connected directly to internal bus 304 may be connected to theinternal bus via either a parallel port 340 or a serial port 342. Otherperipheral devices may be connected to the external programmer viaparallel port 340 or a serial port 342 as well. Although one of each isshown, a plurality of input output (10) ports might be provided. Aspeaker 344 is included for providing audible tones to the user, such asa warning beep in the event improper input is provided by the physician.The telemetry subsystem 322 additionally includes an analog outputcircuit 346 for controlling the transmission of analog output signals,such as IEGM signals output to an EKG machine or chart recorder.

With the programmer 202 configured as shown, a physician or other useroperating the external programmer is capable of retrieving, processingand displaying a wide range of information received from the EKG leadsor from the implantable device 110 and to reprogram the implantabledevice 110 if needed. The descriptions provided herein with respect toFIG. 3 are intended merely to provide an overview of the operation of anexemplary external programmer 202 and are not intended to describe indetail every feature of the hardware and software of the device and isnot intended to provide an exhaustive list of the functions performed bythe device.

It is known that a patient that experiences frequent episodes ofmyocardial ischemia is at a high risk of experiencing a ventricularfibrillation (VF) or some other form of sudden cardiac death. In otherwords, the presence of myocardial ischemia correlates positively with ahigh risk for the development of VF or other forms of sudden cardiacdeath. However, what is not typically known is whether there is a causalrelationship between myocardial ischemic episodes and VF for a specificpatient, and more generally, whether there is a causal relationshipbetween myocardial ischemic episodes and arrhythmias for a specificpatient.

For example, if a device independently monitors for arrhythmias andmyocardial ischemic episodes, and such information is displayedindependently, it would be difficult to determine if there is a causalrelationship between the two. More specifically, if during a period oftime both the frequency of arrhythmias and the frequency of ischemicepisodes increased, it would be difficult to say whether one caused theother, or whether a third factor caused both increases. One way for aphysician to determine whether there is a causal relationship betweenthe myocardial ischemic episodes and arrhythmias if for a physician tomanually and laboriously study an arrhythmia log and a myocardialischemia log in an attempt to see if such events coincide. However, suchmanual analysis may not be practical if such logs contain arrhythmia andischemic episode data relating to numerous such events. Further, aphysician is unlikely to recognize a correlation between ischemic andarrhythmic events unless the physician is specifically looking for suchcorrelation. Thus, the physician may therefore overlook an importantpiece of clinical information, unless such information is brought to thephysician's attention.

Embodiments of the present invention, as will be described below,provide practical ways for determining whether there may be a causalrelationship between myocardial ischemic episodes and arrhythmias. Morespecifically, embodiments of the present invention will enable aphysician to efficiently make determinations of whether myocardialischemic episodes may be precipitating or contributing to the onset ofarrhythmias.

FIG. 4 is a high level flow diagram that is used to summarize specificembodiments of the present invention. In this flow diagram, and otherflow diagrams presented herein, the various algorithmic steps aresummarized in individual “blocks”. Such blocks describe specific actionsor decisions that must be made or carried out as the algorithm proceeds.Where a microcontroller (or equivalent) is employed, the flow diagramspresented herein provide the basis for a “control program” that may beused by such a microcontroller (or equivalent) to effectuate the desiredcontrol of the stimulation device. Those skilled in the art may readilywrite such a control program based on the flow diagrams and otherdescriptions presented herein.

Referring to FIG. 4, at step 402 an implantable system (e.g., a monitor,pacemaker or ICD) is used to monitor for arrhythmias, and as indicatedat step 404 the implantable system is also used to monitor formyocardial ischemic episodes. For example, referring back to FIG. 2, thearrhythmia detector 262 of the implantable device 10 can be used tomonitor for arrhythmias and the ischemia detector 264 can be used tomonitor of myocardial ischemic episodes.

At steps 406 and 408, data indicative of detected arrhythmias and dataindicative of detected myocardial ischemic episodes are stored withinthe implantable system. For example, referring back to FIG. 2, dataindicative of detected arrhythmias and data indicative of detectedmyocardial ischemic episodes can be stored in the memory 294 of theimplantable device 110. Examples of the type of information that may bestored for each detected arrhythmia include: IEGM data corresponding tothe period immediately prior to, during and subsequent to a detectedarrhythmia; the type of arrhythmia (e.g., VT or VF); the discriminatorsused to classify the arrhythmia; whether the discriminators agreed withone another; the rate of the arrhythmia; and time stamp datacorresponding to the beginning and end of each arrhythmia. Examples ofthe type of information that may be stored for each detected myocardialischemic episode include: IEGM data corresponding to the periodimmediately prior to, during and subsequent to a detected myocardialischemic episode; data that identifies the ST-segment level duringvarious portions of an episode (e.g., at onset of the ischemia, the peakof the ischemia and the termination of the ischemia); time stamp datacorresponding to the onset, peak and termination of each ischemicepisode; and the duration of the episode. These are just examples of thetype of data that can be stored. One of ordinary skill in the art willappreciate from this discussion that additional and/or alternative typesof data can also be stored.

At step 410, the arrhythmia and ischemic episode data is telemeteredfrom the implantable device where the data was stored to an externaldevice (e.g., device programmer 202) that can analyze the data. It isnoted that this step is optional, and that some of the following stepscan be performed within the implanted system. However, it is mostefficient and logical for the following steps to be performed outsidethe implanted system, so as to minimize the processing and energyconsumption of the implanted system.

At step 412, for each detected arrhythmia, there is a determination,based on the data, whether there was a myocardial ischemic episodedetected within a specified temporal proximity of (e.g., within apredetermined amount of time of) the arrhythmia. The specified temporalproximity is preferably user programmable, such that a physician candefine this threshold. An exemplary specified temporal proximity is “4hours prior an arrhythmia.” That is, in step 412, for each detectedarrhythmia, there can be a determination of whether there was amyocardial ischemic episode detected during the four hour period leadingup to the arrhythmia. This can be accomplished, for example, bycomparing time stamps of detected arrhythmias to time stamps of detectedmyocardial ischemic events, and identifying those time stamps that arewithin the threshold of one another.

At step 414, when a myocardial ischemic episode is detected within thespecified temporal proximity of a detected arrhythmia, data indicativeof the detected myocardial ischemic episode is linked with the dataindicative of the arrhythmia. This linking is preferably performed insuch a manner that if further information about an arrhythmia isselected for display, further information about the myocardial ischemicepisode that occurred within the specified temporal proximity of thearrhythmia is also displayed, and vice versa.

Embodiments of the present invention also include, as shown in FIG. 5 atstep 502, displaying a log of detected arrhythmias that indicates, foreach arrhythmia, whether there was a myocardial ischemic episodedetected within the specified temporal proximity of (e.g., apredetermined amount of time of) the arrhythmia. Such a log can bedisplayed on the display 314 of the external programmer 202, or anyother computer system that is used to display such information. It isalso possible that such information may be displayed on a print out. Theindicator, specifying that a myocardial ischemic episode was detectedwithin the specified temporal proximity of the arrhythmia, can beaccomplished in numerous ways. For example, the indicator can be a flag,asterisk, note or other similar indicator next to listed arrhythmicevents, or such events can be highlighted, underlined, blinking, or thelike.

At step 504, a user is allowed to select one of the arrhythmias from thelog. For example, using a cursor, mouse, touch screen, or the like, auser is able to select or “click” on an entry in the log so that theycan obtain additional information about a specific arrhythmic event.

As shown at step 506, when a myocardial ischemic event was detectedwithin the specified temporal proximity of a selected arrhythmia,information about the selected arrhythmia and information about themyocardial ischemic episode are displayed for the user. Examples of theinformation about an arrhythmia that can be displayed include: IEGMplots corresponding to the period immediately prior to, during andsubsequent to a detected arrhythmia; the name of the type of arrhythmia(e.g., VT or VF); information about the discriminators used to classifythe arrhythmia; information about whether the discriminators agreed withone another; information about the rate of the arrhythmia; and timinginformation corresponding to the beginning and end of each arrhythmia.Examples of the type of information that may be displayed for amyocardial ischemic episode within the specified temporal proximity tothe selected arrhythmia include: IEGM plots corresponding to the periodimmediately prior to, during and subsequent to a detected myocardialischemic episode; information about the ST segment level during variousportions of an episode (e.g., at onset of the ischemia, the peak of theischemia and the termination of the ischemia); timing informationcorresponding to the onset, peak and termination of each ischemicepisode; information about the amount of time between the ischemicepisode (onset, peak and/or termination) and the arrhythmia; andinformation about the duration of the ischemic episode.

In accordance with the specific embodiments of the present invention,instead of displaying detailed arrhythmia information and ischemiainformation at the same time, whenever one type of information isdisplayed there can be a graphical link to the other type ofinformation. This can be useful where the amount of information to bedisplayed for each type of event (i.e., the arrhythmic event andischemic event) is sufficiently large that a display would be too busyor crowded if all the information were displayed at once.

These are just examples of the type of information that can bedisplayed. One of ordinary skill in the art will appreciate from thisdiscussion that additional and/or alternative types of information canbe displayed for arrhythmias and myocardial ischemic episodes.

If more than one myocardial ischemic episode occurred within thespecified temporal proximity of the selected arrhythmia, all or someinformation about each ischemic episode can be displayed at the sametime, or an indication of the plural episodes can be displayed to theuser, and the user can be allowed to select from a list to obtainfurther information about specific episodes.

Referring now to step 602 of FIG. 6, in certain embodiments of thepresent invention, a log of detected ischemic episodes can be displayedsuch that there is an indication, for each ischemic episode, whetherthere was an arrhythmia detected within a specified temporal proximityof (e.g., four hours following) the ischemic episode. At step 604, auser is allowed to select one of the ischemic episodes from the log, ina similar manner as was discussed above with regards to step 504. Atstep 606, when an arrhythmia was detected within the specified temporalproximity to a selected ischemic event, information about the selectedischemic event and information about the arrhythmia can be displayed forthe user, in a similar manner as was discussed above with reference tostep 506.

The diagrams of FIGS. 5 and 6 explain how information about arrhythmiasand ischemic episodes can be displayed to a user in such a manner that atemporal relationship between the two is immediately apparent to theuser, without requiring that the user (e.g., physician, clinician,technician, etc.) manually and laboriously compare the information abouteach. These diagrams also explain how arrhythmia data and ischemicepisode data can be linked in such a manner that information about oneis easily obtained (e.g., displayed) when viewing information about theother.

FIG. 7 illustrates an exemplary display log 702 of detected arrhythmiasthat can be displayed to a user. In this exemplary embodiment, there isan entire column 704 dedicated to indicating whether there was amyocardial ischemic event within a specified temporal proximity of eacharrhythmia. However, as indicated above, other indicators, such as, butnot limited to, highlighting, underlining, and asterisking, are withinthe scope of the present invention. From the log 702, a user can selecta specific one of the arrhythmias to obtain additional information aboutthe arrhythmia, as well as information about the myocardial ischemicepisode (if one occurred within the specified proximal relationship ofthe selected arrhythmia). In one embodiment, a user can select (e.g.,click on) the ischemic event indicator, and detailed information aboutthat ischemic event can be immediately displayed.

Similarly, if a user was observing a myocardial ischemic episode log,there would be an indicator that specifies whether an arrhythmiaoccurred within the specified temporal proximity of each ischemicepisode. A user can select a specific one of the episodes to obtaininformation about the ischemic episode, as well as information about thearrhythmia (if one was within the specific proximal relationship of theselected ischemic episode). In one embodiment, a user can select (e.g.,click on) the arrhythmia indicator, and detailed information about thatarrhythmia can be immediately displayed.

FIG. 8 illustrates an exemplary graph 802 that enables a physician tosee, at a glance, those periods of time (e.g., days) during which bothan ischemic episode and an arrhythmia occurred. In the exemplary graph802, an “x” indicates that an arrhythmia occurred on a specific day andan “o” illustrates that an ischemic event occurred on a specific day. Ifboth an arrhythmia and an ischemic event occurred the same day, then the“x” and the “o” overlap or overlay one another, as shown at 804. In oneembodiment, a user can select (e.g., click on) a day in the graph 802,and detailed information about event(s) that occurred on that day can bedisplayed. Where both an arrhythmia and an ischemic event occurred onthe same day (or within some other specified temporal proximity),information about both events and their temporal proximity to oneanother can be displayed when that day is selected.

In accordance with a further embodiment, summary diagnostics can bepresented to a physician. For example, a display may indicate how manyarrhythmias out of a total number of arrhythmias during a specificperiod of time (e.g., a month) occurred within a specified temporalproximity of an ischemic episode. This can be presented, e.g., as N outof M arrhythmias occurred within the specified temporal proximity of anischemic episode. Alternatively or additionally, this can be presentedas a percentage of arrhythmias that occurred within the specifiedtemporal proximity of an ischemic episode. One of ordinary skill in theart reading this description will realize that other manners ofproviding summary diagnostics are within the spirit and scope of thepresent invention. Such summary diagnostics can also be trended so aphysician could see over a period of time (e.g., the life of animplantable device), whether there was a change in the correlationbetween ischemia and arrhythmia.

As mentioned above, the specified temporal proximity can be userprogrammable. In accordance with embodiments of the present invention,when a user changes the temporal proximity (i.e., specifies a newtemporal proximity of interest), an updated arrhythmia and/or myocardialischemic episode log, graph and/or summary diagnostic(s) can be producedand displayed to a user. For example, the specified temporal proximitycan first be defined such that a myocardial ischemic episode isidentified if it occurred within the four hours prior to an arrhythmia.A user may then change the temporal proximity to identify a myocardialischemic episode that occurred within the six hours prior to anarrhythmia. Assuming there were some detected arrhythmias that did nothave a myocardial ischemic episode in the four hours leading up to thearrhythmia, but did have a myocardial ischemic episode in the six hoursleading up to the arrhythmia, then the log or graph (that includesindicators of whether there was a myocardial ischemic episode within thespecified temporal proximity of the arrhythmia) and summary diagnostics(e.g., that indicates a percentage of arrhythmias that occurred withinthe specified temporal proximity) will change accordingly.

Alternative embodiments of the present invention can be use with animplantable system that does not include an ischemia detector 264. Insuch embodiments, an implantable system is used to monitor forarrhythmias and to store, within the implantable system, data indicativeof a detected arrhythmia and data indicative of a specified periodleading up to the arrhythmia. Such data is then transmitted(periodically, or when the patient visits a physician's office) from theimplantable system to a non-implanted system. For each arrhythmia, thenon-implanted system can then determine based on the data indicative ofthe specified period leading up to the arrhythmia, whether a myocardialischemic episode occurred within the specified period leading up to thearrhythmia.

Embodiments of the present invention analyze and optionally display datain such a manner that it is immediately apparent when myocardialischemic episodes and arrhythmias may be correlated. More specifically,embodiments of the present invention can be used to identify myocardialischemic episodes that may precipitate an arrhythmia. Preferably,embodiments of the present invention present such information to a userin such a manner that the user need not manually and laboriously comparearrhythmia information with myocardial ischemia information. Embodimentsof the present invention can also be used to link arrhythmia data andischemic episode data in such a manner that information about one iseasily obtained (e.g., displayed) when viewing information about theother.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have often been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the claimed invention. For example, it would bepossible to combine or separate some of the steps shown in FIGS. 4-6.Further, it is possible to change the order of some of the steps shownin FIGS. 4-6, without substantially changing the overall events andresults.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the embodiments ofthe present invention. While the invention has been particularly shownand described with reference to preferred embodiments thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method for determining whether there is acorrelation between arrhythmias and myocardial ischemic episodesexperienced by a patient, comprising: using an implantable system tomonitor for arrhythmias and to monitor for myocardial ischemic episodes;storing, within the implantable system, data indicative of detectedarrhythmias and data indicative of detected myocardial ischemicepisodes; communicating information regarding detected arrhythmias anddetected myocardial ischemic episodes from the implantable system to anexternal device; for each detected arrhythmia, determining, based on thedata, whether there was a myocardial ischemic episode detected within aspecified time before the arrhythmia; and displaying on an externaldisplay an indicator that a detected arrhythmia and a detectedmyocardial ischemic episode occurred within the specified time of eachother.
 2. The method of claim 1, wherein the determining step isperformed by the implantable system.
 3. The method of claim 1, whereinthe data stored at the storing step is transmitted from the implantablesystem to the external device, and wherein the determining step isperformed by the external device.
 4. The method of claim 1, furthercomprising: when a myocardial ischemic episode is detected within thespecified time before a detected arrhythmia, linking data indicative ofthe myocardial ischemic episode with data indicative of the arrhythmia.5. The method of claim 1, further comprising: displaying a log ofdetected arrhythmias that indicates, for each arrhythmia, whether therewas a myocardial ischemic episode detected within the specified timebefore the arrhythmia.
 6. The method of claim 1, further comprising:displaying a log of detected myocardial ischemic episodes thatindicates, for each episode, whether there was an arrhythmia within thespecified time of the episode.
 7. The method of claim 6, furthercomprising: allowing a user to select one of the myocardial ischemicepisodes from the log; and when an arrhythmia was detected within thespecified time of the selected myocardial ischemic episode, displayinginformation about both the selected myocardial ischemic episode and thearrhythmia.
 8. The method of claim 1, further comprising: displaying,based on the data, information indicative of each arrhythmia for which amyocardial ischemic episode was detected within the specified time ofthe arrhythmia, and information indicative of each myocardial ischemicepisode that was detected within the specified time of the arrhythmia.9. The method of claim 1, wherein: the using step includes monitoring anIEGM signal sensed by the implantable device; the storing step includesstoring IEGM data for each detected myocardial ischemic episode and eachdetected arrhythmia; and further comprising displaying IEGM informationfor each arrhythmia for which a myocardial ischemic episode was detectedwithin the specified time of the arrhythmia, and IEGM information foreach myocardial ischemic episode that occurred within the specified timeof the arrhythmia.
 10. The method of claim 1, wherein: the storing stepincludes storing timing data for each detected myocardial ischemicepisode and each arrhythmia; and the determining step includes for eachdetected arrhythmia, determining, based on the timing data, whetherthere was a myocardial ischemic episode detected within the specifiedtime of the arrhythmia.
 11. The method of claim 1, further comprising:determining what percentage of detected arrhythmias during a period oftime occurred within the specified time of an ischemic episode; anddisplaying the determined percentage.
 12. The method of claim 1, furthercomprising: determining what number of detected arrhythmias, out of atotal number of detected arrhythmias during a period of time, occurredwithin the specified time of an ischemic episode; and displaying thedetermined number and the total number.